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Transparent ITO as a Metal Stack in KTH’s FDSOI CMOS Technology
KTH, School of Electrical Engineering and Computer Science (EECS).
2025 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Transparent electronics is an emerging field concentrating on invisible circuitry. A nearly transparent complementary metal oxide semiconductor (CMOS) technology can be a novel solution for optoelectronic and lab-on-chip applications. Indium tin oxide (ITO) is known to be electrically conductive (ρ = 100 μΩcm) [1] and optically transparent (> 85%) [2]. This study is focused on using ITO as a metal stack for fully-depleted silicon-on-insulator (FDSOI) CMOS technology. ITO is shown to meet the compatibility requirements on fabrication for CMOS technology. Annealing ITO with 5% N2/H2 at 450 C for 30 seconds after deposition is shown to decrease local sheet resistance down to 5 Ω/□and improve the sheet resistance uniformity across the wafer up to 95%. Inductively-coupled plasma reactive ion etching (ICP-RIE) is selected to be the primary method to etch ITO with CH4/Cl2/H2 chemistry. A wafer with a poly-Si gate and an ITO metal layer is successfully transferred onto a glass substrate, demonstrating near transparency to visible light. An FDSOI CMOS wafer with a single 200 nm ITO metal layer is fabricated with a 25 nm active silicon device layer and a 100 nm p-type poly-Si gate. ITO to ITO contacts and ITO to gate contacts are tested with a probe station, contacts were found to have 35 Ω and 5 kΩ of resistance, respectively. The lowest subthreshold swing (SS) value was found to be 130 mV/dec and VT was higher than 1 V.

Abstract [sv]

Transparent elektronik är ett framväxande område som koncentrerar sig på att realisera osynliga kretsar. En nästan transparent komplementär metalloxidhalvledarteknik (CMOS) teknologi kan förbättra prestandan för optoelektroniska och lab-on-chip-applikationer. Indiumtennoxid (ITO) är elektriskt ledande (ρ  100 μΩcm) [1] och optiskt transparent (>85%) [2]. Denna studie är fokuserad på att använda ITO som en metallstack för att sammankoppla transistorer i en en helt utarmad kisel-på-isolator (FDSOI) CMOS-teknik. ITO fanns uppfylla kompatibilitetskraven för tillverkning av FDSOI CMOS . Värmebehandling av ITO med 5% N2/H2 vid 450 C i 30 sekunder minskar lokalt ytresistansen till 5 Ω/□ och förbättrar uniformiteten av ytresistansen över skivan till 95%. Induktivt kopplad plasmareaktiv jonetsning (ICP-RIE) valdes som den primära metoden för att etsa ITO med en CH4/Cl2/H2-kemi. En med ett poly-Si lager och ett ITO-metallskikt överfördes framgångsrikt till ett glassubstrat med nästan full transparens för synligt ljus. En FDSOI CMOS-skiva med ett 200 nm ITO-metalllager tillverkades med ett 25 nm aktivt kisellager och en 100 nm p-typ poly-Si gate. ITO till ITO-kontakter och ITO till gate-kontakter testades elektriskt och hade 35 Ω respektive 5 kΩ resistans. Den lägsta subthreshold swing (SS) hos transistorerna var 130 mV/dec och VT var runt 1 V.

Place, publisher, year, edition, pages
2025. , p. 77
Series
TRITA-EECS-EX ; 2025:5
Keywords [en]
Transparent Electronics, Fully Depleated Silicon-on-Insulator (FDSOI), Complementary Metal Oxide Semiconductor (CMOS), Indium Tin Oxide (ITO), Annealing
Keywords [sv]
Transparent Elektronik, Komplementär Metalloxidhalvledarteknik (CMOS), Helt Utarmad Kisel-på-Isolator (FDSOI), Indiumtennoxid (ITO), Värmebehandling
National Category
Computer and Information Sciences
Identifiers
URN: urn:nbn:se:kth:diva-361821OAI: oai:DiVA.org:kth-361821DiVA, id: diva2:1948690
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Available from: 2025-04-08 Created: 2025-03-31 Last updated: 2025-04-08Bibliographically approved

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